When laying a fiber web (hereinafter referred to as web) onto an output conveyor, the laying arm of the cross lapper performs a pivoting movement, wherein its lower, free end moves in close distance over the output conveyor transversely to the transport direction of the latter. If the upper end of the laying arm is pivotally attached on a pivotally mounted supply arm, the supply arm also performs a pivoting movement. A cross lapper of this type, also referred to as a camel back cross lapper, is generally known and, for instance, is described in the book “Vliesstoffe”, Verlag Wiley-VCH, Weinheim, 2000 (page 160).
In known camel back cross lappers, the lower end of the laying arm is coupled to a carriage which is movably guided on rails transversely to the transport direction of the output conveyor. The carriage is connected to a drive means so that by the aid of this drive means, the pivoting movement of the laying arm, and possibly of the supply arm, is carried out.
The speed at which the web is discharged by the laying arm of the cross lapper may be more than 200 m/mm, but speeds in the range of 300 m/mm are desirable. The free end of the laying arm must therefore move correspondingly fast over the output conveyor to prevent disturbing the material and the creation of folds in the layered web. These high speeds lead to problems caused by aerodynamic effects. A web section layered by the laying arm may lift off its base and start fluttering under the influence of aerodynamic pull. One approach to alleviate this effect has been to provide a garnished pressure roller which felts the fibers of the freshly layered fiber web with the fibers of the web layers already layered arranged underneath. Since a laying arm usually discharges fiber web in both of its movement directions, two such pressure rollers may be mounted at the laying arm, increasing the weight of the laying arm accordingly. Further, the effect caused by such pressure rollers is relatively moderate.